In many designs of nuclear reactor installations, a steam generator is associated with the reactor. Communication between the steam generator and the reactor is through a so-called steam generator nozzle, typically connecting the steam generator at a level below the normal levels of water maintained in the reactor and its refueling pool. In such installations, it is necessary, from time to time to gain access to the interior of the steam generator to enable maintenance to be performed. For these occasions, it is necessary to reduce the water level temporarily in the reactor and refueling pool enabling a temporary dam to be installed in the generator nozzles. Once the nozzle is dammed, isolating the reactor and refueling pool from the steam generator, the reactor and refueled pool can be refilled to normal levels.
It has been known, heretofore, to employ for this purpose, a two-part frame structure, which can be disassembled, brought into the steam generator through a "man way" provided in the wall thereof. After being moved into the interior of the generator, the two-part frame structure is reassembled and fitted with an inflatable peripheral seal and integral diaphragm. The dam is then inserted into the opening of the generator nozzle and may be temporarily positioned therein by mechanical means. The peripheral inflatable seal is then inflated, pressing tightly against the sidewalls of the generator nozzle to form a seal.
It is always a concern, of course, that a leak or rapture may form in the pneumatically inflated seal, and therefore conventional nozzle dam structures frequently employ redundant seals. This naturally adds to the complication and expense of the unit.
In accordance with the present invention, a new and improved nozzle dam arrangement is provided which, while constructed generally in accordance with known principles, employs a significantly superior and improved form of pneumatically inflatable sealing arrangement, which forms a highly effective isolation seal in the generator nozzle, yet obviates the need for redundant pneumatic seals. To this end, the apparatus of the invention incorporates a continuous peripheral flap seal, which is displaceable radially by an inflatable peripheral element. When the nozzle dam is initially positioned within the generator nozzle, and the pneumatic peripheral element is pressurized, the continuous flap seal is pressed radially outward, into tight sealing engagement with the cylindrical wall of the nozzle. By orienting the free end of the continuous flap seal toward the pressurized side, the flap seal becomes self-holding as a function of the unbalanced water pressure acting thereon from the reactor and refueling pool.
While it is intended and contemplated that the peripheral inflatable element will remain pressurized at all times, should a fault develop and the element become depressurized, the flap seals of the invention device will remain operative and continue to afford an effective dam seal.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment and to the accompany drawings.